1. Field of the Invention
The present invention relates to a method of manufacturing resin particles.
2. Description of the Related Art
An image forming apparatus for forming images electrophotographically includes a photoreceptor, a charging section, an exposure section, a developing section, a transfer section, a fixing section, and a cleaning section. The charging section charges the surface of the photoreceptor. The exposure section irradiates a signal light to the surface of the photoreceptor in a charged state to form static latent images corresponding to image information. The developing section supplies a toner in a developer to the static latent images formed on the surface of the photoreceptor to develop the static latent images thereby forming toner images. The transfer section transfers toner images formed on the surface of the photoreceptor to a recording material. The fixing section fixes the transferred toner images to the recording material. The cleaning section cleans the surface of the photoreceptor after transfer of the toner images. In such an image forming apparatus, static latent images are developed by using a one-component developer containing a toner, or a two-component developer containing a toner and a carrier as the developer to form images. The toner used herein is a resin particles formed by dispersing and granulating a colorant and a wax as a release agent in a binder resin as a matrix.
Since the image-forming apparatus using the electrophotographic system can form images of good image quality at a high speed and a reduced cost, it is utilized, for example, in copying machines, printers, and facsimile units and recent popularization of the image forming apparatus in an electrophotographic manner is remarkable. In accordance with this, severer demands are directed to the image forming apparatus. Particularly, it has been particularly considered important for images formed by the image forming apparatus higher fineness, higher resolution and stabilization of image quality and increased image forming speed. For attaining them, it is indispensable to investigate from both the aspects of image forming process and developer.
For higher finesses and higher resolution of images, reduction of size of toner particles is one of the subjects to be solved from a view point that accurate reproduction of static latent images is important with respect to the developer. As a method of manufacturing toner particles of a reduced diameter, an emulsifying aggregation method has been known for instance. In the emulsifying aggregation method, toner particles are manufactured by forming resin particles containing a resin binder, a colorant, and a release agent, etc in an aqueous medium such as water and aggregating the resin particles.
The emulsifying aggregation method includes, for example, a melt kneading emulsifying aggregation method. In the melt kneading emulsifying aggregation method, a raw material containing a resin binder, a colorant a release agent, etc. is at first melt kneaded, and the molten kneaded product is cooled to solidify. Then, the solidified molten kneaded product is pulverized, charged in an aqueous medium and then stirred in the aqueous medium, whereby a pulverizate of the molten kneaded product is dispersed in the aqueous medium to obtain resin particles. In this case, bubbles are generated by stirring by a stirring section and the generated bubbles are sometimes attached to the surface of the pulverizate of the molten kneaded product. When the bubbles are attached to the surface of the pulverizate of the molten kneaded product, a surfactant for dispersing the pulverizate of the molten kneaded product into the aqueous medium cannot act on the surface of the pulverizate of the molten kneaded product to result in a problem that the pulverizate of the molten kneaded product cannot be dispersed sufficiently in the aqueous medium.
In view of the problem described above, a method of manufacturing a toner with an aim of preventing the generation of bubbles is proposed (refer, for example, to Japanese Unexamined Patent Publication JP-A 2005-173263). In the technique disclosed in JP-A 2005-173263, a liquid dispersion as an aqueous medium containing a dispersoid containing a toner raw material is applied with a deaerating treatment of deaerating the liquid dispersion by using a depressurizing method of putting the liquid dispersion in an atmosphere, preferably, at 80 kPa or lower and, more preferably, from 0.1 to 40 kPa, and then the liquid dispersion is jetted from a discharging aperture at a diameter of about from 5 to 500 μm to finely granulate the dispersoid. The method of manufacturing the toner disclosed in JP-A 2005-173263 is, a technique of removing bubbles and gases dissolved in the liquid dispersion by applying the deaerating treatment.
However, in the method of manufacturing the toner disclosed in JP-A 2005-173263, since energy applied in the deaerating treatment is small, it result in a problem that bubbles and dissolved gases cannot sufficiently be removed from the aqueous medium. For the bubbles, while macro bubbles that can be recognized, for example, by visual observation can be removed, smaller micro bubbles cannot be sufficiently removed from the surface of the dispersoid. In a case where the micro bubbles cannot be removed from the surface of the dispersoid, the action sites of the surfactant at the surface of the dispersoid are decreased, and fine granulation and particle size control cannot be conducted by the dispersion of the dispersoid in the aqueous medium.
In a case where the bubbles or the dissolved gases are present in the aqueous medium, the bubbles or dissolved gases generate cavitation (hereinafter occasionally referred to as “cavitation phenomenon”) to generate bubbles in the aqueous medium. Since the portion where bubbles are generated is at a lower pressure than that at the periphery thereof, an energy due to external force for fine granulation is consumed for crushing the generated bubbles. Accordingly, the external force cannot be applied effectively to the dispersoid and no sufficient fine granulation can be conducted. Further, in a case where a dispersoid, particularly, a dispersoid at micron to sub-micron size is finely granulated in the aqueous medium by applying external force, when bubbles are attached to the surface of the dispersoid, since the surfactant cannot wet the dispersoid, no sufficient fine granulation can be conducted when the dispersoid is finely granulated by applying external force in an aqueous medium.